1. Field of the Invention
The present invention relates to an arm structure for an articulated mechanism, and more particularly to such a mechanism having a plurality of articulated links comprising accumulators.
2. Description of the Prior Art
There have recently been proposed various articulated mechanisms, such as industrial robots or the like, which comprise articulations actuatable under hydraulic pressure. One example of such an articulated mechanism is disclosed in Japanese Laid-Open Patent Publication No. 52-69152.
Many hydraulically operated articulated mechanisms employ an accumulator with a view to reducing the capacity of a hydraulic pressure source used for supplying a hydraulic pressure to the articulated mechanism. Since the accumulator is in the form of a heavy high-pressure container, it cannot be installed in a movable member such as an articulated arm of the mechanism, but has to be mounted on an immovable member. The articulated mechanism also includes many hydraulic motors associated with the respective articulations for actuating the articulated arms and directional control valves for controlling the hydraulic motors. If only one accumulator is used, those hydraulic motors which are located remotely from the accumulator may not be operated smoothly since a certain time delay is inevitable in receiving the hydraulic pressure from the accumulator. It has been impossible to provide accumulators to be combined respectively with the hydraulic motors because of the large weight of the accumulators.
Where the articulations are connected in series with each other, oil passages are required to deliver high-pressure working oil from the common hydraulic pressure source successively to the motors which are sequentially arranged from the proximal end of the articulations and also to deliver the working oil back to a tank. Since these oil passages are normally arranged along the articulated arms, they take up a large space and so does the accumulator. Consequently, the entire articulated mechanism is large in size.